In what cases is it preferable to directly call another service for integration?

Direct invocation of another service for integration is preferred in the following cases:

• When low latency and high performance are required, as direct calls are usually faster than asynchronous methods.
• If the interaction is simple and does not require complex processing or message routing.
• When an immediate response is needed (synchronous interaction), for example, for data requests or operations that influence subsequent logic.
• In systems with low load and a limited number of services, where complex integration mechanisms are redundant.

Example: an authentication service directly calls the user service to verify data.

However, when scaling and architecture complexity increase, asynchronous approaches or message buses are often used to enhance resilience and flexibility.